The shock wave, caused as an aircraft passes through the speed of sound, remains attached to the aircraft as long as the aircraft is supersonic. Its position relative to the aircraft will change as the aircraft Mach number increases, but it is always there.
It doesn’t matter how long the aircraft has been supersonic, the shock wave stays with it, and if it passes over you, your ears will detect the sudden pressure change as the sound we call the boom. Actually it will probably be heard as a double boom as there are two main shock waves, the bow wave and the tail wave. How loud the boom seems to you will depend mainly on how close you are to the aircraft at the time.
At very low supersonic speeds the boom may not reach the ground, and occasionally during turning or decelerating flight the boom can appear stronger at some points on the ground than others, but, unfortunately, it is always there. This is the main reason that most, but not all, countries have banned overflight by civilian aircraft at supersonic speeds.
The turbulent wake an aircraft leaves behind it varies with several factors. It is true that, for various reasons, a subsonic jet may well generate more turbulence on approach, when it is flying slowly, than it does in cruise, when it is flying faster.
This does not mean that when comparing the amount of wake turbulence caused by two different aircraft, flying at vastly different cruising speeds, one subsonic and the other supersonic, that you may assume that the faster aircraft will cause less turbulence.
Concorde will be travelling around two and a half times faster than the subsonic jet and will cause substantially more wake turbulence. If you want to believe otherwise, feel free.